Embodiments of the invention generally relate to method, apparatus or device, and system for error handling e.g. in a packet switched network or structure such as general packet radio service, GPRS. Further, embodiments of the invention may generally relate to core networks, CN, and connectivity.
A traditional user plane flow is shown in FIG. 2. As illustrated in FIG. 2, a packet data connection between a radio network (e.g. UTRAN/RNC, universal mobile telecommunication system terrestrial radio access network/radio network controller) and a core network usually goes via a serving general packet radio service, GPRS, support node, SGSN.
A basic idea in a direct tunnel solution is that the serving node, SGSN, is left out in user plane operation after a packet data connection (e.g. using a packet data protocol, PDP, context) has been set up between the radio network and the packet core network. This direct tunnel functionality is a known functionality which is also called “one tunnel” functionality and is described in specification 3GPP TS 23.060 V7.3.0 (2006-12). A direct tunnel is an optional function e.g. in Iu mode that allows the SGSN to establish a direct user plane tunnel between the radio access network, RAN, and a apparatus GPRS support node, GGSN, within the packet-switched, PS, domain. When a direct tunnel is established (SGSN indicates direct tunnel establishment to GGSN) the GGSN usually sets RNC's address and tunnel endpoint identifier, TEID, as user plane destination for data packets. Thus, when a direct tunnel user plane has been set up as shown in attached FIG. 3, the packet data connection to the radio network (UTRAN/RNC) is established directly between the radio network controller of the radio access network and the gateway GPRS support node, GGSN. In FIG. 3, SGSN is not shown but may be involved in establishing the tunnel in control plane. A direct tunnel capable SGSN has the capability to be configured on a per GGSN and per RNC basis irrespective of whether or not it can use a direct user plane connection. The SGSN handles the control plane signalling and makes the decision when to establish a direct tunnel.
When a radio access bearer, RAB, assigned for a packet data protocol context is released (i.e. the context is preserved) a tunnel such as a general packet radio service tunnel protocol tunnel for the user plane, GTP-U, tunnel is established between the GGSN and SGSN in order to be able to handle the downlink packets. The letter “U” stands for user plane which serves for transmitting user traffic such as data. The control signaling is handled by the control plane. A bearer release situation is shown in FIG. 4 corresponding to FIG. 15.6-1, idle mode handling, of the standard TS 23.060. There are further conditions in which a direct tunnel should not or no longer be used in following traffic cases such as roaming or a specific subscription or lack of support.
Standards specification TS 23.060 contains a description of user plane protocol stack and definitions which are included hereinto by reference. Section 5.6.2 describes the user plane (Iu mode). Section 5.6.2.1 is directed to the MS, mobile station, -GGSN user plane with GERAN, GSM/EDGE Radio Access Network, in Iu mode. Section 5.6.2.2 illustrates the MS-GGSN user plane with UTRAN. Generally, a packet data convergence protocol (PDCP) is a transmission functionality which maps higher-level characteristics onto the characteristics of the underlying radio-interface protocols. The packet data convergence protocol provides protocol transparency for higher-layer protocols, and supports e.g. internet protocol version 4, IPv4, PPP and internet protocol version 6, IPv6. The packet data convergence protocol provides protocol control information compression.
The GPRS tunnelling protocol, GTP, for the user plane (GTPU) tunnels user data between a radio access network such as a universal mobile telecommunication system terrestrial radio access network, UTRAN, and a third generation, 3G, serving GPRS support node, SGSN, and between GPRS support nodes, GSNs, in the backbone network. The GTP-U, GPRS Tunnelling Protocol-user plane; is a protocol that provides packet transmission and reception services to user plane entities in the gateway GPRS support node (GGSN), the serving GPRS support node (SGSN), and the radio network controller (RNC). The GTP-U is defined for the Gn interface between gateway support nodes (GSN) within a public land mobile network (PLMN), for the Gp interface between GPRS support nodes, GSNs in different public land mobile networks, and for the Iu interface between the serving GPRS support node (SGSN) and the UMTS terrestrial radio access network (UTRAN). UMTS stands for Universal Mobile Telecommunications System. The GTP encapsulates all PDP packet data units, PDUs. An SGSN controls the user plane tunnel establishment and may establish a direct tunnel between UTRAN and GGSN as shown in FIG. 3. User datagram protocol/Internet protocol, UDP/IP, are backbone network protocols used for routeing user data and control signalling. A Radio Link Control, RLC, protocol provides logical link control over the radio interface. There may be several simultaneous RLC links per mobile station, MS. Each link is identified by a bearer identifier, Id. A Medium Access Control (MAC) protocol controls the access signalling (request and grant) procedures for the radio channel. The user plane between GPRS support nodes is the same as for A/Gb mode.
A protocol data unit, PDU, is transferred between different protocol stacks. The actual information to be transmitted end-to-end is carried in PDUs. A tunnel endpoint identifier, TEID, is an identifier that unambiguously identifies a tunnel endpoint in the receiving GPRS tunnelling protocol (GTP) entity. Usually, the receiving end of a GTP tunnel locally assigns the TEID value the transmitting side must use.
Usually, when an RNC/BSC fails, all its RNC/BSC contexts affected by the failure become invalid and should be deleted. When no direct tunnel exists and the RNC/BSC receives a GTPU PDU from an SGSN for which no radio access bearer, RAB, context exists, the RNC/BSC may discard the GTPU PDU and return a GTP error indication to the originating SGSN. The SGSN may locally release the radio access bearer but should preserve the associated PDP context. The SGSN may initiate an RAB Assignment procedure in order to re-establish the radio access bearer.
However, when a direct tunnel has been established, this error handling does not function as the next contact point in user plane is the GGSN, not SGSN.